Relay system



E.FmEDLANDER RELAY SYSTEM Filed March 9, 1958 NEY INVENTOR l 7zeaZanakniikmh Sept 2,1941.

Patented Sept. 2, 1941 UNITED STATES PATENT OFFICE RELAY SYSTEMApplication March 9, 1938, Serial No. 194,863 In Germany March 10, 19379 Claims.

This invention relates to a control system and it has particularrelation to a relay control system energized through a tuned circuit.

In the design of a relay, one of the major problems is to provide arelay both with a sensitive response and a response that remainsaccurate and reliable. If an electromagnetic relay is employed, acondenser may be connected in series with the winding of the relay andtuned to respond to a predetermined condition of an alternating currentcircuit. Such a system, though sensitive, is not entirely satisfactoryfor the reason that the winding of the electromagnetic relay changes itsimpedance during actuation, thereby varying the tuning of the relaysystem.

Resonant circuits may be employed which do not change theircharacteristics during relay actuation provided separate iron core chokecoils and series condensers are employed. If a choke coil in a resonantcircuit for relay actuation is given a direct current premagnetizationdependent on the potential of a tuning condenser from a rectifierconnected in series with the resonant circuit, stable operation may beobtained. Such 3 systems, however have the disadvantage of requiring anumber of additional elements, such as choke coils and rectifiers.

According to my invention, a control system is provided wherein a tunedor resonant circuit is employed for actuating a switch or relay devicehaving an actuating element which does not change the inductance orcapacitance of the tuned circuit during the actuation of the device. Forthis purpose, a thermal switch or relay has been found suitable. Thethermal switch may have an actuating element comprising a wire or abimetallic unit which, when heated, changes in dimension to operate theswitch contacts. Such a system does not change its inductance orcapacitance during actuation, the actuating element being, in effect, aconstant resistance.

Accordingly, it is an object of my invention to provide a sensitivecontrol unit having an accurate and reliable actuating system.

It is also an object of my invention to provide a control relay systemhaving a tuned energizing system associated with a relay actuatingelement which, during actuation, does not vary the tuning of theenergizing system A further object of my invention is to provide acontrol relay system employing a thermally actuated relay controlled bya tuned circuit.

Another object of my invention is toprovide an accurate and sensitivecontrol system responsive to two different values of a variablecondition.

A still further object of my invention is to provide a tuned controlsystem for maintaining a variable condition accurately between twopredetermined limits.

Other objects of my invention will be apparent from the followingdescription taken in conjunction with the accompanying drawing, inwhich:

Figure l is a diagrammatic view of a thermally actuated relay associatedwith a tuned control circuit;

Fig. 2 is a graphic representation of the voltage-current relationshipsin the control system of Fig. 1;

Fig. 3 is a diagrammatic view of a modification of the circuit of Fig.1;

Figs. 4, 5 and 6 are diagrammatic views of various modifications ofcircuits responsive to two different conditions of an alternatingcurrent circuit; and,

Fig. 7 is a graphic representation of the voltage current relationshipsof the circuit illustrated in Fig. 6.

Referring to the drawing, Figure 1 depicts a tuned circuit comprising acapacitance l and a choke coil or inductance 2 having an iron coreconnected in series across the conductors L1 and L2 of an alternatingcurrent circuit. A relay 3 has an actuating element 4 connected inparallel with the capacitance.

As pointed out above, the relay actuating element 4 is so selected thatits impedance remains constant during the actuation of the relay, and athermal actuating element has been found desirable for this purpose.During actuation the thermal element 4 moves a pivoted contact member 5into engagement with a fixed contact member 6. A pair of outputterminals 1, 8 are provided for the control system, and are connectedrespectively to the fixed contact member 6 and the conductor L2.

The iron core choke coil 2 and the capacitance I are so proportioned asto produce the voltagecurrent relationships shown in Fig. 2, whereinvoltage is represented by ordinates and current by abscissae. Thevoltage across the choke coil 2 with respect to the current flowingtherethrough is shown by a curve EL, the voltage across the capacitance(shown above the current axis for convenience) by a curve (Ec), and theresultant voltage across the tuned circuit by a curve E. It will benoted that the resultant voltage curve E has a voltage-currentrelationship such that the current increases slowly with respect tovoltage cuit.

L1, L2 will be accompanied by a large increase of current through thetuned circuit and by an accompanying large increase of voltage acrossthe capacitance I. Since the relay 3 is responsive to the voltage acrossthe capacitance I, such an increase of voltage positively energizes therelay to close its contact members 5, 6. Any device to be controlled bythe relay 3 may be connected to the outputterminals 1, 8.

Although the relay 3 of Fig. 1 responds to a change in voltage, it maybe connected to respond to other Variable conditions. For ex.-

ample, if it is desired to have the relay respond to the temperature ofa furnace, the temperature may be employed for controlling analternating voltage which is supplied to a relay system similar to thatshown in Fig. 1. If it is desired to have the relay respond to currentchanges, the current may be passed through a resistance, and the voltagedrop across the resistance may be employed for energizing the aboverelay system. Since-tuned circuits may be designed to providean'appreciable current change in response to a variation in frequency, asimilar relay system may be designed for actuation in accordance withthe frequency of an alternating current cir- If the frequency andvoltage of an alternating-current circuit both vary and it is desired tomake the relay responsive to voltage only, a voltage proportional to thefrequency change may be introduced in series with the tuned circuit. 1

Although the actuating element t of the relay 3 in Fig. 1 is in parallelwith the capacitance I, it may be connected in series with the tunedcircuit as shown in Fig. 3 wherein the reference characters let to 8acorrespond respectively to the reference characters I to 8 of Fig. 1.For some purposes the parallel connection of Fig. 1

is preferable for the reason that higher voltages may be applied to theactuating element to. It should be noted'in Fig. 3 that the currentflowing through the terminal la. also flows through the actuatingelement to of the relay. Consequently, once the relay operates to closeits contacts ta, 6a, a holding circuit is established for the actuatingelement la through the load I across the terminals la, 8a.

Instead of a. single fixed contact member 6, a pair of fixed contactmembers maybe employed with each of the relays 3, one being contacted bythe movable member 5 when the actuating element t is deenergized, andthe other being contacted by the movable element ii when the actuatingelement :3 is energized. Each of the fixed contacts may be employed forcontrol purposes.

,It is also possible to connect a plurality of relays for response to,different conditions of an alternating-currentcircuit. For example, Fig.4 illustrates a system designed to maintain a certain variable, such asvoltage, between two predetermined limits. In Fig. 4, a capacitance lb,2,

' choke coil 22) and a relay 3%; are connected berelay 3c, which issimilar in construction to the relay 3, is connected with its actuatingelement to in series with a tuned parallel circuit 9, comprising acapacitance l0 and an iron core choke coil II, across the conductors L1,L2. The fixed contact member to of this relay 3cis connected to aterminal 12.

. The first relay 3b is adjusted to close its contact members when thevoltage across the conductors L1, L2 rises above a predetermined value,Whereas the tuned circuit 9 is proportioned to increase the currentthrough, and actuate the relay 30 when the voltage across the conductorsL1, L2 falls below a predetermined value. The output from these relays3b, 30 may be employed for controlling a motor 13, which may be theoperating motor for a voltage regulator such as a step transformer. Themotor it may be a two-phase motor having a central lead connected to theterminal 8b, and two outer leads connected to the terminals lb, i2.Across the two outer leads of the motor i3, a condenser ii is connectedfor controlling the phase relationships in the two windings of themotor.

Under operating conditions, if the motor I3 is connected to theconductors L1, L2 through the terminals lb, 8?), it will rotate in onedirection, whereas if the motor is connected through the terminals 8b,!2, it will rotate in the opposite direction and may be used thereforefor increasing or lowering the voltage across the conductors L1, L2 tocompensate for any departure of this voltage from a predetermined value.

In some cases it has been found desirable to control the rate ofreopening of the contact members of the relays 3b, to. For this purposean auxiliary relay 3d, similar to the relay 3, may have its actuatingelement 40!, connected between the fixed contact member 6b of the relay3b and the conductor L2. Because of this connection, the contact members5d, Ed of the relay 3d will be closed when the contact members 52), 6bof the relay 3'0 are closed. The contact members 5d, 6d are connectedbetween the fixed contact member 51) and the lower end of the actuatingelement ib of the relaylib. Consequently, whenever the contact members501, 6d close in response to a closure of the contact members of therelay 3b, the actuating element 4b of the relay 3?) will be shortcircuited through the contact members 5d, 6d, and the current whichheats the actuating member ib consequently will be diminished.

- Ordinarily a direct short circuit would decrease the current throughthe actuating element lbjtoo greatly, and for this reason a resistancemember J5 is'connected in series with the contact mem-' bers 5d, 6d;Because of the decrease incurrent flowing through the actuating element"4b, the relay contact members 5b, 6b will tend to reopen somewhat morerapidly. If the increase in po tential across the conductors L1, L2 isvery large, the current through the actuating element 4b of the relay 3bis strong enough to keep the contact members 5b, to closed despite theaction of the relay 3d, and the motor l3 consequently will runcontinuously. But if the potential variation is relatively small, theaction of the relay 3d will cause the contact members 5b, 6b to reopenafter a brief interval and result in intermittent operation of the motorit. A similar relay 3D and resistance element l5 are shown for thethermal actuating element 40 of the relay 30.

In order to protect the contact of the relays "against the effects ofhigh voltage, a condenser I6 may be connected across each pair ofcontacts.

This is particularly desirable if the contacts are enclosed in a vacuum.

Because of the tuned circuits made up of the iron core choke coils andcapacitances, the control of the thermal relays is very sensitive andaccurate. Therefore, the low voltage and high voltage relays of Fig. 4may be adjusted so that the difference between their operating limits isvery small;

It is also possible to operate two different relays at different valuesof a variable condition by means of one tuned circuit. For example, inFig. 5 a capacitance l1 and a chock coil I8 are connected in seriesacross the conductors L1, L2. Two relays 3e and [9 are provided foractuation by the voltage across the condenser II. The first relay 3c issimilar to those previously described, and is connected to be actuatedwhen a variable condition, such as voltage, of the conductor L1, L2rises above a predetermined value.

The second relay l9 has a pair of normally closed contact members 20,2|. Energization of the actuating element 22 of this relay opens thecontact members 2!], 2| and the circuit associated with them. Theactuating element 22 is con- By varying the tap 24 the operating pointsof I the relays 3e, 19 may be controlled as desired. Since adisplacement of the tap 24 introduces resistance in series with one ofthe actuating elements while reducing the resistance in series with theother actuating element, the total resistance across the capacitance lltends to remain constant.

A second adjustment is provided by connecting a second divider 25 acrossa portion of the choke coil [8, the divider having a movable tap 26 conThe fixed contact nected to the conductor L2. members 6e, 2| of therelays 3e, l9 are connected respectively to terminals 1e and l2e and athird terminal Be is connected to the line L2.

These three terminals 16, 8e and l2e correspond to the terminals lb, Bband I2 shown in Fig. 4.

Another relay system that is energized from a single tuned circuit isshown in Fig. 6. In this arrangement a capacitance 2! and a choke coil28 are connected in a series tuned circuit across the conductors L1, L2.A pair of relays 3 3g, which are similar to those shown in Figs. 1 to 4,are connected for energization from this tuned circuit. The first relay3f has its actuating element 4 1 connected directly across thecapacitance 21. The second relay 3g has its actuating element 49'connected across the capacitance 21 and a portion 29 of the choke coil28.

The voltage-current relationships of the circuit shown in Fig. 6 areapparent from a study of Fig. '7 wherein ordinates represent voltage,and abscissae represent current flowing through the series circuitcomprising the capacitance 21 and choke coil 28. In this figure threevoltage curves are shown; one VL for the voltage across the choke coil23, a second (Vc) for the voltage across the capacitance 21 (shown abovethe current axis for convenience), and a third V which represents thevoltage across the portion of the choke coil 29 employed for actuatingthe relay 3g. If the relays are exactly alike, the circuit containingthe capacitance 27 and choke coil 28 is so proportioned that for anormal current In the voltage across the capacitance 21, represented bythe ordinate ab, is equal to the voltage bc across the capacitance plusthat portion 29 of the choke coil employed for actuating the relay 39.

If the voltage across the conductors L1, L2 decreases, the currentthrough the tuned circuit also decreases, but the voltage be employedfor energizing the relay 39 increases to a value bc, as shown in Fig. 7,sufficient for actuating the relay 3g.

If the voltage across the conductors L1, L2 increases, the currentflowing through the capacitance 21 and choke coil 28 also increases, andthe voltage ab across the capacitance increases to a value a bsuflicient for actuating the relay 3). Therefore, the arrangement ofFig. 6 may be employed similarly to the arrangement shown in Figs. 4 and5, the output terminals If, 8 and 12 of Fig. 6 corresponding to theterminals lb, 8b and I2 of Fig. 4.

If the relay 3c of Fig. 4 were replaced by a normally closed relaysimilar to the relay I9, shown in Fig. 5, the energizing circuit for therelay 3 could be similar to that employed for the relay 3b. In such amodification, a decrease in the voltage across the conductors L1, L2would deenergize the modified relay 30, thereby closing the contactmembers of the modified relay. The action of the auxiliary relay 3d insuch a case should be modified to increase the current fiowing in theactuating element of the modified relay 30.

An auxiliary relay may be employed for increasing or decreasing thecurrent flowing in the actuating element of any of the relays shown inFigs. 5 and 6 in a manner analogous to the employment of the relay 3d ofFig. 4. Protective condensers similar to the condenser l8 of Fig. 4 alsomay be employed for these other relays.

Although I have described my invention with reference to certainspecific embodiments thereof, it is to be understood that my inventionis not limited to the specific circuits, elements and arrangementsdisclosed, but is to be limited only by the appended claims asinterpreted in view of the prior art.

I claim as my invention:

1. In a control system; a source of alternating energy; a plurality ofelectroresponsive control devices, each of said control devices having athermal actuating element; and energizing means, including at least onetuned circuit for energizing said actuating elements from said source,said energizing means including impedance means adjustable fordecreasing the flow of energy to one of said actuating elements andsimultaneously increasing the flow of energy to another of saidactuating elements.

2. In a relay system, a source of alternating energy, a tuned circuitconnected for energization from said source, said tuned circuitincluding a capacitance member and an inductance member, a firstelectroresponsive device having a thermal actuating element connectedfor energization in accordance with the voltage across said capacitancemember, and a second electroresponsive device having a thermal actuatingelement connected for energization in accordance with the resultantvoltage across said capacitance member and a portion of said inductancememher.

3. In a control system, a source of alternating energy, a firstelectroresponsive control device having a thermal actuating element, a'series tuned circuit for energizing said actuating element from saidsource, a tuned parallel circuit, and a second electroresponsive controldevice having a thermal actuating element connected for energizationfrom said source through said tuned parallel circuit.

4. In a relay system; a source of alternating energy, a first relaydevice having a pair of normally open contacts and a thermally actuatedclosing element; a second relay device having a pair of normally closedcontacts and a thermally actuated'opening element; and energizing means,including at least one tuned circuit, for energizing said thermalelements from said source.

5. In a control system, a source of alternating current subject tovariation from a predetermined condition, an electroresponsive controldevice having fixed-impedance actuating means, and tuned circuitenergizing means for supplying energy from said source to said actuatingmeans, said electroresponsive control device including control meanseffective When the variation of said source is in one direction andadditional control means effective when the Variation of said source isin the opposite direction from said predetermined condition.

6. In a control system, a source of alternating current subject tovariation from a predetermined voltage, an electroresponsive controldevice having fixed-impedance actuating means, and tuned circuitenergizing means for supplying energy from'said source to said actuatingmeans, said electroresponsive control device including control meansoperative when the voltage of said source increases beyond apredetermined point, and additional control means operative when thevoltage of said source decreases beyond a predetermined point, saidenergizing means being more effective for variations beyond one of saidpredetermined points than for variations adjacent said predeterminedvoltage.

'7. In a control system, a source of alternating current, a tunedcircuit energized from said source, said tuned circuit including aninductive reactance and a capacitive reactance in series; and anelectroresponsive device having a fixedimpedance actuating elementconnected across only one of said reactances.

8. In a control system, a source of alternating current, a tuned circuitenergized from said source, said tuned circuit including an inductivereactance and a capacitive reactance, and an electroresponsive devicehaving a plurality of thermal actuating elements connected forenergization in accordance With the condition of one of said reactances,said actuating elements being energized to different degrees.

9. In a control device for an alternating current system; a circuithaving a non-linear voltampere characteristic; control means;fixed-impedance, heat-responsive actuating means for said control meansincluding an electrical resistance heater element; means for passingelectrical current flowing through at least part of said circuitdirectly through said electricalv resistance heater element forsupplying heat to said actuating means, said actuating means beingresponsive to heat developed by said electrical cur rent flowing in saidelectrical resistance heater element for operatin said control means;and means responsive to an operation of said control means for varyingthe impedance offered to said electrical current.

